Smoking articles such as cigarettes or cigars produce sidestream smoke during static burning, i.e. when the smoking article is idle and not being drawn upon by the smoker. The Surgeon General has determined that sidestream smoke is more of a concern than smoke exhaled by a smoker. Sidestream smoke tends to create a smoky atmosphere in closed quarters that may impair vision and is often considered objectionable visually. Sidestream smoke also can be physically irritating, causing a burning sensation in the eyes, nose and throat.
Smoke is a dispersion of solid and liquid particles carried by combustion gases and air. Smoke particles consist of carbon-rich moieties such as tar and soot, water vapor, and oxides of inorganic compounds that result from incomplete combustion. These moieties act as smoke nuclei, initiating condensation and forming smoke. Hornby and Watson, (Magnesium Hydroxide--a Combined Flame Retardant and Smoke Suppressant Filler for Thermoplastics Plastics and Rubber Processing and Applications 6:169-175 (1986)) describe plastic polymer combustion and smoke formation as a three step process. In phase one polymer is thermally degraded to simple fuel consisting of polymer fragments and pyrolysis products. In phase two the simple fuels are converted to reactive aromatic intermediates that subsequently form either stable polycyclic aromatic hydrocarbons or smoke nuclei. In phase three smoke nuclei coagulate and agglomerate to form smoke particles. Magnesium hydroxide provides a high surface area where carbon deposits and subsequently is volatilized during and after flame extinction to reduce the number of smoke formation.
Many attempts to reduce sidestream smoke have been made. For example, magnesium hydroxide (Mg(OH).sub.2) has been used commercially in cigarette paper to reduce visible sidestream smoke in cigarettes. Mg(OH).sub.2 decomposes to MgO at ca. 360.degree. C., with a concomitant increase in surface area. U.S. Pat. No. 4,805,644 to Hampl teaches that sidestream smoke reduction is related to the surface area of cigarette wrapper paper filler. Some patents relating to sidestream smoke reduction are as follows.
U.S. Pat. No. 4,420,002 to Cline is directed to a cellulosic wrapper for tobacco that contains 5% to 50% magnesium hydroxide filler having a median particle size of less than 10 micrometers, and an unreactive magnesium oxide filler. The magnesium hydroxide filler is preferably added to the fiber pulp furnish, thus maximizing contact between fiber and filler.
U.S. Pat. No. 4,450,847 to Owens is directed to a cellulosic wrapper containing an amorphous gel of magnesium hydroxide freshly precipitated on the fibers of the sheet as a filler, plus unreactive magnesium oxide, calcium carbonate or both as co-filler(s). The wrapper also contains 2% to 8% by weight potassium acetate as a chemical adjuvant. The '847 patent describes methods of adding filler material during the process of making cigarette paper.
U.S. Pat. No. 4,881,557 to Martin is directed to cigarette paper that incorporates a mixture of freshly precipitated magnesium hydroxides having a median particle size of about 15 micrometers. The magnesium hydroxide is precipitated externally and subsequently added to the paper's fibers. This is in contrast to previous methods, such as the method of the '847 patent noted above wherein in situ precipitation is employed. The '557 patent teaches that increasing levels of magnesium hydroxides over 15% is not feasible because smoking articles such as cigarettes made with wrapping paper containing high percentages of magnesium hydroxide self-extinguish or are non-combustible. The '557 patent also describes methods of adding filler material during the process of making cigarette paper.
U.S. Pat. No. 4,915,118 to Kaufman et. al. is directed to a reduced smoke wrapper containing freshly precipitated magnesium hydroxide filler precipitated by an equal or near equal stoichiometric addition rate process in the presence of particulate magnesium hydroxide and/or calcium co-fillers, and in the absence of cellulosic pulp fibers.
Despite the above-described effort, there is still a need for reducing the amount of smoke produced by burning articles, and in particular, reducing the amount of smoke produced by burning cigarettes.